Combined heat and power plants (referred to as CHP plants below) of the type mentioned above are known in different variants, for example from the documents listed below                DE 33 33 828 A1        DE 25 00 641 C2        DE 31 16 624 C2        DE 4 203 491 A1        DE 3 044 666 A1        
These plants are based on internal combustion engines, which are coupled to electrical generators and are operated in housings which practically communicate with the atmosphere surrounding them and are thus at atmospheric pressure inside.
These housings are used primarily for thermal and sound insulation of the CHP plant, in order to achieve the highest possible degree of utilisation of the primary energy used and of the waste heat while at the same time keeping sound emissions as low as possible.
A particularly efficient solution for a thermal and sound-insulating housing of a CHP plant is also known from DE 101 51 121 B 4.In contrast to the solutions already generally known, in this case an airtight casing which is resistant to overpressure is provided in addition to the thermal and sound insulation. This casing is then constantly subjected to an elevated internal pressure using the generator fan propeller or an additional fan/compressor. As a result of the airtight housing, no warm internal air can escape from the housing. Thermal losses in connection with the thermal insulation can thereby be minimised. The disadvantage of this solution however consists in that, as a result of the elevated internal pressure according to the invention, absolute airtightness of the casing must be achieved, otherwise warm internal air can escape permanently into the surrounding atmosphere and thus additional thermal losses occur.
For the manufacture of such an airtight and pressure-resistant casing including the necessary pipeline holes for the primary energy, cooling water feed and return lines, exhaust gas line, electrical cables and control cables, this means a high level of technological complexity, with corresponding manufacturing costs.
The invention is then based on the object of specifying a further improved housing for a CHP plant, having a more effective thermal and sound insulation effect, which ensures the best possible utilisation of the primary energy used and an even more efficient utilisation of the waste heat of the internal combustion engine and of the generator and in the process manages with minimal investment and operating costs.